Negative pressure conditioning device and forced air furnace employing same

1. A pneumatic signal conditioning device configured to provide a conditioned pressure signal representing a pressure drop across a heat exchanger, the pneumatic signal conditioning device comprising:

a first fluid path comprising a first inlet and a first outlet, the first fluid path configured such that the first outlet provides a first conditioned signal representing a burner box pressure at the first inlet;

a second fluid path comprising a second inlet and a second outlet, the second fluid path configured such that the second outlet provides a second conditioned signal representing a collector box pressure at the second inlet;

a third fluid path disposed between the first fluid path and the second fluid path, thereby providing fluid communication between the first fluid path and the second fluid path; and

wherein a difference between the first conditioned signal and the second conditioned signal represents the pressure drop across the heat exchanger.

2. The pneumatic signal conditioning device of claim 1 , wherein the first fluid path comprises an internal flow restriction.

3. The pneumatic signal conditioning device of claim 1 , wherein at least one of the first inlet and the first outlet comprise a conditioning orifice.

4. The pneumatic signal conditioning device of claim 3 , wherein the first inlet comprises a first inlet conditioning orifice and the first outlet comprises a first outlet conditioning orifice.

5. The pneumatic signal conditioning device of claim 1 , wherein the second fluid path comprises an internal flow restriction.

6. The pneumatic signal conditioning device of claim 1 , wherein at least one of the second inlet and the second outlet comprise a conditioning orifice.

7. The pneumatic signal conditioning device of claim 6 , wherein the second inlet comprises a second inlet conditioning orifice and the second outlet comprises a second outlet conditioning orifice.

8. The pneumatic signal conditioning device of claim 1 , further comprising a bleed orifice disposed within the third fluid path.

9. The pneumatic signal conditioning device of claim 1 , further comprising a fourth fluid path disposed between the first fluid path and the second fluid path, thereby providing fluid communication between the first fluid path and the second fluid path.

10. The pneumatic signal conditioning device of claim 9 , further comprising a fixed bleed orifice disposed within the third fluid path.

11. The pneumatic signal conditioning device of claim 10 , further comprising an adjustable bleed orifice disposed within the fourth fluid path.

12. A forced-air furnace comprising:

a heat exchanger having an upstream port and a downstream port;

a burner configured to burn fuel and provide combustion products to the heat exchanger;

a gas valve configured to provide fuel to the burner, the gas valve comprising a first pressure port and a second pressure port; and

a pneumatic signal conditioning device comprising:

a first fluid path comprising a first inlet and a first outlet, the first fluid path configured such that the first outlet provides a first conditioned signal representing a pressure at the first inlet; and

a second fluid path comprising a second inlet and a second outlet, the second fluid path configured such that the second outlet provides a second conditioned signal representing a pressure at the second inlet;

wherein the first inlet is in fluid communication with the upstream port, the second inlet is in fluid communication with the downstream port, the first outlet is in fluid communication with the first pressure port and the second outlet is in fluid communication with the second pressure port such that a difference between the first outlet and the second outlet provides to the gas valve a conditioned pressure signal representing a pressure drop across the heat exchanger.

13. The forced-air furnace of claim 12 , wherein the upstream port is proximate the burner.

14. The forced-air furnace of claim 12 , further comprising a collector box positioned proximate the downstream port.

15. A negative pressure conditioning device for use with a forced air furnace having a gas valve, a burner manifold and a collector box, the negative pressure conditioning device comprising:

a first gas valve port adapted to be in fluid communication with the gas valve, a first conditioning orifice contained within the first gas valve port;

a second gas valve port adapted to be in fluid communication with the gas valve, a second conditioning orifice contained within the second gas valve port;

a burner manifold port adapted to be in fluid communication with the burner manifold, a burner manifold conditioning orifice contained within the burner manifold port; and

a collector box port adapted to be in fluid communication with the collector box, a collector box conditioning orifice contained within the collector box port.

16. A pneumatic signal conditioning device configured to provide a conditioned pressure signal representing a pressure drop across a heat exchanger, the pneumatic signal conditioning device comprising:

a first fluid path comprising a first inlet and a first outlet, the first fluid path configured such that the first outlet provides a first conditioned signal representing a burner box pressure at the first inlet;

a second fluid path comprising a second inlet and a second outlet, the second fluid path configured such that the second outlet provides a second conditioned signal representing a collector box pressure at the second inlet;

a reference vent in fluid communication with at least one of the first fluid path and the second fluid path; and

wherein a difference between the first conditioned signal and the second conditioned signal represents the pressure drop across the heat exchanger.

17. The pneumatic signal conditioning device of claim 16 , wherein the reference vent is also in fluid communication with an atmosphere exterior to the pneumatic signal conditioning device.